Light emitting semiconductor device that has advantages of low power consumption, less heat generation, long life, small size, impact tolerance, high speed, free mercury and good optical performance has been applied as a light source with steady waive length to an electronic device. The brightness and operation life of a LED device has been tremendously improved along with the development of the optical technology, and may serve as the primary light source of an electronic device in the future.
For example, a light emitting diode (LED) device with white light is made by a LED die encapsulated by a phosphor compound mixed with at least one phosphor, whereby the phosphor is activated by a portion of the blue light emitting from the LED die to derived the blue light into yellow, and the yellow light is then mixed with the other portion of the blue light to produce white light emitting from the LED device.
Conventionally, the steps for coating the phosphor compound on to the LED die are conducted in the device packaging process. During the packaging process, a die should be mounted on to a substrate prior the phosphor compound is coated thereon. However, since the phosphor compound is directly blanket over the LED die, the phosphor mixed in the fluid compound may be precipitated to the periphery of the LED die during the compound coating process. Furthermore the fluid compound may be aggregated the lateral side of the LED die, so as the resulting LED package may have a horizontal thickness greater than the vertical thickness thereof. Thus the initial blue light provide by the LED die and the yellow light derived by the phosphor can not be mixed adequately so as to make the lateral emitting light of the LED package having a color temperature different from light vertically emitting form the LED package, and the brightness of the LED package may be decreased.
To resolve these problems, an advanced method has been applied. FIGS. 1A to 1F illustrate cross-sectional views of a LED packaging process in accordance with a conventional packaging method. First pluralities of LED die units 100 are flip and mounted on a substrate, such as a silicon substrate 101. A conformal coating process, such as screen painting or a thick film process, is then conducted to form a photoresist layer 103 over the substrate 101 and the LED die units 100, and a plurality of openings 104 are formed in the photoresist layer 103 by a patterning process to expose these LED die units 100. Subsequently, a compound 105 mixed with phosphor is filled into the openings 104. A backing process is then conducted prior the photoresist layer 103 is peeled. The packaged LED die units are then separated from the substrate 101; and each of the die units 100 is bonded with wires to from a LED device.
However, the mounting steps may affect the accuracy for aligning LED die units 100 mounted on the substrate 101 with the openings 104 formed in the photoresist 104 during the LED device batch manufacturing process. The phosphor compound may not encapsulate the LED die in equilibrium. Thus light provided by the resulting LED device may have an undesired color temperature, so that the brightness of the LED device is still decreased, also the heat-dispersing efficiency of the LED device may be reduced by the disequilibrium of phosphor compound coated on the LED die.